1. Field of the Invention
The present invention relates to a compact, low-consumption, sensitive optical device using a photonic crystal, and a method of determining an optimum angle of a light beam incident on the photonic crystal such that the light beam can be deflected at a large deflection angle by the photonic crystal.
2. Disclosure of the Prior Art
Photonic crystal is of an artificial multidimensional periodic structure obtained by periodically arranging at least two materials having different dielectric constants at an interval substantially equal to the wavelength of light. In the expectation that the photonic crystal would remarkably enhance the control of light, it is being vigorously developed as the next generation optical equipment.
As an optical switch using the photonic crystal, for example, an optical switch is disclosed in Japanese Patent Early Publication [kokai] No. 10-90634. As shown in FIG. 20, this optical switch is for switching between the ON position (transmission) where a light beam incident on the photonic crystal (=incident light beam) is allowed to pass through the photonic crystal, and the OFF position (reflection) wherein the light beam is reflected from the photonic crystal to prevent the transmission of the light beam.
That is, light beams provided from a pair of optical fibers 110a, 110b are incident on the photonic crystal 100 through collimator lenses 120a, 120b and polarizers 130a, 130b. This optical switch comprises a means for irradiating a control light 150 to the photonic crystal 100 through a circular polarizer 140. The irradiation of the control light 150 causes a change in a photonic band gap structure of the photonic crystal 100, so that it becomes possible to switch between the ON and OFF positions. In the ON position, the transmitted light beam passing through the photonic crystal 100 is output through a pair of polarizers 160a, 160b. 
Thus, since the purpose of this optical switch is to switch between the ON position for allowing the light beam to pass through the photonic crystal and the OFF position for reflecting the light beam from the photonic crystal, it merely provides the presence or absence of the transmitted light beam as the output. Therefore, this limits the application areas of the optical switch.
If the light beam incident on the photonic crystal can be deflected at a large angle, this technique will be fit for a wide range of uses such as compact, low-consumption optical devices and variable optical attenuator (VOA). In addition, according to the deflection phenomenon of the light beam by the photonic crystal, when an energy change in the photonic crystal is caused by an environment change around the photonic crystal, a change in deflection angle of the light beam occurs. By detecting this change in deflection angle, it is expected to sense the environment change with a high resolution. Thus, it has a great potential for improving detection accuracy of the optical sensor.